There is often a need to identify a target in a target-rich environment. An example is when a traveler is arriving at an airport to be greeted by unknown hosts. Typically, the hosts hold up a paper sign with the traveler's name printed on it. Possible disadvantages of this system are lack of anonymity: all persons in the vicinity can read the traveler's name on the paper sign; there might be many such signs, often hand written and sometimes not very legible; it is relatively easy for a malicious third party to hold up a sign with the traveler's name to misdirect the traveler or to approach the host and purport to be the named traveler.
Therefore, a means of providing a more discreet but publicly visible means of alerting a target is highly desirable.